2-Trifluoromethyl-5-(1-alkylthio)alkylpyridines are useful intermediates for the preparation of certain new insecticides; see, for example, U.S. Patent Publications 2005/0228027 and 2007/0203191. Alkylthioenamines are useful intermediates for preparing 2-trifluoromethyl-5-(1-alkylthio)alkyl-pyridines; see, for example, U.S. Patent Publication 2008/0033180 A1. Alkylthioenamines can, in turn, be prepared by reacting an alkylthio substituted aldehyde with an anhydrous disubstituted amine. The alkylthio substituted aldehyde starting materials are difficult to obtain in high purity and are often contaminated with thioacetal and aldol condensation impurities. It would be desirable to have a process for preparing alkylthio substituted aldehydes in good yield and high purity.